U.S. patent number 6,650,235 [Application Number 09/892,499] was granted by the patent office on 2003-11-18 for method and apparatus for recognizing object.
This patent grant is currently assigned to Denso Corporation. Invention is credited to Keiji Matsuoka, Yoshie Samukawa, Noriaki Shirai.
United States Patent |
6,650,235 |
Shirai , et al. |
November 18, 2003 |
Method and apparatus for recognizing object
Abstract
A transmission wave is applied to a predetermined range in a
width-wise direction of a subject vehicle. Objects located ahead of
the subject vehicle are recognized on the basis of reflected waves
which result from reflections of the transmission wave. The
reflected waves are converted into a received signal. Detection is
made regarding a variation in an intensity of the received signal
along a direction corresponding to the width-wise direction of the
subject vehicle. The received signal is separated into a first
signal portion and a second signal portion on the basis of the
detected signal intensity variation. The first signal portion
corresponds to a scattered portion of the transmission wave. The
second signal portion corresponds to an unscattered portion of the
transmission wave. Objects are recognized on the basis of the
second signal portion.
Inventors: |
Shirai; Noriaki (Kariya,
JP), Samukawa; Yoshie (Kariya, JP),
Matsuoka; Keiji (Kariya, JP) |
Assignee: |
Denso Corporation (Kariya,
JP)
|
Family
ID: |
18705119 |
Appl.
No.: |
09/892,499 |
Filed: |
June 28, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Jul 10, 2000 [JP] |
|
|
2000-208559 |
|
Current U.S.
Class: |
340/435;
359/196.1; 342/70; 340/436; 356/21; 701/301; 356/4.01; 340/903;
342/54 |
Current CPC
Class: |
G01S
17/931 (20200101); G01S 7/4802 (20130101); B60Q
9/008 (20130101); G01S 2013/9323 (20200101); G01S
2013/932 (20200101) |
Current International
Class: |
B60Q
1/50 (20060101); B60Q 1/52 (20060101); G01S
17/93 (20060101); G01S 17/00 (20060101); G01S
7/48 (20060101); G01S 13/93 (20060101); G01S
13/00 (20060101); B60Q 001/00 () |
Field of
Search: |
;340/435,436,901,903,904,933,942 ;701/301 ;342/70,54,118,71,72
;356/342,4.01,4.02-4.1,20,21,72 ;359/196,197,204 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tong; Nina
Attorney, Agent or Firm: Posz & Bethards, PLC
Claims
What is claimed is:
1. A method of applying a transmission wave to a predetermined
range in a width-wise direction of a subject vehicle, and
recognizing objects located ahead of the subject vehicle on the
basis of reflected waves which result from reflections of the
transmission wave, the method comprising the steps of: converting
the reflected waves into a received signal; detecting a variation
in an intensity of the received signal along a direction
corresponding to the width-wise direction of the subject vehicle;
separating the received signal into a first signal portion and a
second signal portion on the basis of the detected signal intensity
variation, the first signal portion corresponding to a scattered
portion of the transmission wave, the second signal portion
corresponding to an unscattered portion of the transmission wave;
and recognizing objects on the basis of the second signal
portion.
2. An object recognition apparatus comprising: laser radar means
for applying a transmission wave to a predetermined range in a
width-wise direction of a subject vehicle, converting reflected
waves, which result from reflections of the transmission wave, into
a received signal, and detecting objects on the basis of the
received signal; and recognizing means for recognizing objects
located ahead of the subject vehicle on the basis of results of
detection by the laser radar means; wherein the recognizing means
comprises: 1) means for detecting a variation in an intensity of
the received signal along a direction corresponding to the
width-wise direction of the subject vehicle; 2) means for
separating the received signal into a first signal portion and a
second signal portion on the basis of the detected signal intensity
variation, the first signal portion corresponding to a scattered
portion of the transmission wave, the second signal portion
corresponding to an unscattered portion of the transmission wave;
and 3) means for recognizing objects on the basis of the second
signal portion.
3. An object recognition apparatus as recited in claim 2, wherein
the recognizing means comprises means for detecting the intensity
of the received signal, and means for executing the separation of
the received signal into the first signal portion and the second
signal portion on the basis of the detected signal intensity.
4. An object recognition apparatus as recited in claim 3, wherein
the recognizing means comprises means for setting a threshold value
equal to a peak value of the detected signal intensity minus a
predetermined value, means for determining whether or not the
detected intensity of the received signal is lower than the
threshold value, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion in response to a result of determining whether or not the
detected intensity of the received signal is lower than the
threshold value.
5. An object recognition apparatus as recited in claim 2, wherein
the recognizing means comprises means for calculating a rate of the
detected signal intensity variation, and means for executing the
separation of the received signal into the first signal portion and
the second signal portion in response to the calculated intensity
variation rate.
6. An object recognition apparatus as recited in claim 5, wherein
the recognizing means comprises means for setting a threshold value
with respect to the calculated intensity variation rate
corresponding to a predetermined steep state, means for determining
whether or not the intensity of the received signal is lower than
the threshold value, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion in response to a result of determining whether or not the
intensity of the received signal is lower than the threshold
value.
7. An object recognition apparatus as recited in claim 5, wherein
the recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
8. An object recognition apparatus as recited in claim 5, wherein
the recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state occurring in a prescribed vehicle
width-wise direction position, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
9. An object recognition apparatus as recited in claim 5, wherein
the recognizing means comprises means for calculating a straight
line approximate to the rate of the detected signal intensity
variation in a least-squares method, means for calculating a slope
of the straight line, and means for calculating the rate of the
detected signal intensity variation from the calculated slope of
the straight line.
10. An object recognition apparatus as recited in claim 2, wherein
the recognizing means comprises means for setting a threshold value
with respect to the intensity of the received signal, means for
using the threshold value in the separation of the received signal
into the first signal portion and the second signal portion, and
means for changing the threshold value on the basis of a size of a
recognized object.
11. An object recognition apparatus as recited in claim 10, wherein
the recognizing means comprises means for continuing the changing
of the threshold value until a length of the recognized object in
the width-wise direction of the subject vehicle falls into a
predetermined range.
12. An object recognition apparatus as recited in claim 2, wherein
the received signal contains a pulse, and a time difference between
a leading edge and a trailing edge of the pulse increases as the
intensity of the received signal rises, and wherein the recognizing
means comprises means for estimating the intensity of the received
signal on the basis of the time difference between the leading edge
and the trailing edge of the pulse.
13. An object recognition apparatus as recited in claim 2, wherein
the recognizing means comprises condition estimating means for
estimating whether or not there occurs a scatter condition that the
transmission wave can be scattered, means for, only when the
condition estimating means estimates that there occurs the scatter
condition, executing the separation of the received signal into the
first signal portion and the second signal portion.
14. An object recognition apparatus as recited in claim 13, wherein
the scatter condition comprises a condition that a waterdrop can
meet a member of the radar means through which the transmission
wave travels.
15. An object recognition apparatus as recited in claim 14, wherein
the condition estimating means comprises means for estimating
whether or not there occurs the scatter condition on the basis of
whether or not a windshield wiper of the subject vehicle is
active.
16. A recording medium storing a program for controlling a computer
operating as the recognizing means in the object recognition
apparatus of claim 2.
17. A method of applying a transmission wave to a predetermined
range in a width-wise direction of a subject vehicle, and
recognizing objects located ahead of the subject vehicle on the
basis of reflected waves which result from reflections of the
transmission wave, the method comprising the steps of: converting
the reflected waves into a received signal; wherein an intensity of
a part of the transmission wave is maximized at a transmission
center point, and is decreased as the part of the transmission wave
becomes more distant from the transmission center point as viewed
along the width-wise direction of the subject vehicle, and wherein
a portion of the transmission wave which has an intensity equal to
or higher than a prescribed intensity is effective for object
recognition; detecting a rate of a variation in an intensity of the
received signal along a direction corresponding to the width-wise
direction of the subject vehicle; separating the received signal
into a first signal portion and a second signal portion on the
basis of the detected intensity variation rate, the first signal
portion corresponding to the portion of the transmission wave which
has the intensity equal to or higher than the prescribed intensity,
the second signal portion corresponding to another portion of the
transmission wave; and recognizing objects on the basis of the
first signal portion.
18. A method of applying a transmission wave to a predetermined
range in a width-wise direction of a subject vehicle, and
recognizing objects located ahead of the subject vehicle on the
basis of reflected waves which result from reflections of the
transmission wave, the method comprising the steps of: converting
the reflected waves into a received signal; wherein an intensity of
a part of the transmission wave is maximized at a transmission
center point, and is decreased as the part of the transmission wave
becomes more distant from the transmission center point as viewed
along the width-wise direction of the subject vehicle, and wherein
a portion of the transmission wave which has an intensity equal to
or higher than a prescribed intensity is effective for object
recognition; setting a threshold value with respect to an intensity
of the received signal; separating the received signal into a first
signal portion and a second signal portion on the basis of the
threshold value, the first signal portion corresponding to the
portion of the transmission wave which has the intensity equal to
or higher than the prescribed intensity, the second signal portion
corresponding to another portion of the transmission wave;
recognizing objects on the basis of the first signal portion; and
changing the threshold value until a length of a recognized object
in the width-wise direction of the subject vehicle falls into a
predetermined range.
19. An object recognition apparatus comprising: laser radar means
for applying a transmission wave to a predetermined range in a
width-wise direction of a subject vehicle, converting reflected
waves, which result from reflections of the transmission wave, into
a received signal, and detecting objects on the basis of the
received signal; and recognizing means for recognizing objects
located ahead of the subject vehicle on the basis of results of
detection by the laser radar means; wherein an intensity of a part
of the transmission wave is maximized at a transmission center
point, and is decreased as the part of the transmission wave
becomes more distant from the transmission center point as viewed
along the width-wise direction of the subject vehicle, and wherein
a portion of the transmission wave which has an intensity equal to
or higher than a prescribed intensity is effective for object
recognition; wherein the recognizing means comprises: 1) means for
detecting a rate of a variation in an intensity of the received
signal along a direction corresponding to the width-wise direction
of the subject vehicle; 2) means for separating the received signal
into a first signal portion and a second signal portion on the
basis of the detected intensity variation rate, the first signal
portion corresponding to the portion of the transmission wave which
has the intensity equal to or higher than the prescribed intensity,
the second signal portion corresponding to another portion of the
transmission wave; and 3) means for recognizing objects on the
basis of the first signal portion.
20. An object recognition apparatus as recited in claim 19, wherein
the recognizing means comprises means for setting a threshold value
with respect to the calculated intensity variation rate
corresponding to a predetermined steep state, means for determining
whether or not the intensity of the received signal is lower than
the threshold value, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion in response to a result of determining whether or not the
intensity of the received signal is lower than the threshold
value.
21. An object recognition apparatus as recited in claim 19, wherein
the recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
22. An object recognition apparatus as recited in claim 19, wherein
the recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state occurring in a prescribed vehicle
width-wise direction position, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
23. An object recognition apparatus as recited in claim 19, wherein
the recognizing means comprises means for calculating a straight
line approximate to the rate of the detected signal intensity
variation in a least-squares method, means for calculating a slope
of the straight line, and means for calculating the rate of the
detected signal intensity variation from the calculated slope of
the straight line.
24. An object recognition apparatus comprising: laser radar means
for applying a transmission wave to a predetermined range in a
width-wise direction of a subject vehicle, converting reflected
waves, which result from reflections of the transmission wave, into
a received signal, and detecting objects on the basis of the
received signal; and recognizing means for recognizing objects
located ahead of the subject vehicle on the basis of results of
detection by the laser radar means; wherein an intensity of a part
of the transmission wave is maximized at a transmission center
point, and is decreased as the part of the transmission wave
becomes more distant from the transmission center point as viewed
along the width-wise direction of the subject vehicle, and wherein
a portion of the transmission wave which has an intensity equal to
or higher than a prescribed intensity is effective for object
recognition; wherein the recognizing means comprises: 1) means for
setting a threshold value with respect to an intensity of the
received signal; 2) means for separating the received signal into a
first signal portion and a second signal portion on the basis of
the threshold value, the first signal portion corresponding to the
portion of the transmission wave which has the intensity equal to
or higher than the prescribed intensity, the second signal portion
corresponding to another portion of the transmission wave; 3) means
for recognizing objects on the basis of the first signal portion;
and 4) means for changing the threshold value until a length of a
recognized object in the width-wise direction of the subject
vehicle falls into a predetermined range.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of recognizing an object.
In addition, this invention relates to an apparatus for recognizing
an object which can be mounted on a vehicle. Furthermore, this
invention relates to a recording medium storing a computer program
for recognizing an object.
2. Description of the Related Art
A known object recognition apparatus for a vehicle emits a forward
wave beam such as a light beam or a millimeter wave beam from the
body of the vehicle, and enables the forward wave beam to scan a
given angular region in front of the body of the vehicle. In the
case where an object exists in the given angular region, the
forward wave beam encounters the object before being at least
partially reflected thereby. A portion of the reflected wave beam
returns to the apparatus as an echo wave beam. The apparatus
detects and recognizes the object in response to the echo wave
beam.
The known object recognition apparatus is used in a warning system
for a vehicle which alarms when an obstacle such as a preceding
vehicle exists in a given angular region in front of the present
vehicle. The known object recognition apparatus is used also in a
system for a vehicle which controls the speed of the vehicle to
maintain a proper distance between the vehicle and a preceding
vehicle.
It is known to use a laser beam as a forward wave beam in an object
recognition apparatus for a vehicle. In general, the front end of
such an object recognition apparatus has a transparent member
through which the forward laser beam travels. A waterdrop
encounters the transparent member, changing into a lens-like shape
thereon. In some cases, the forward laser beam is scattered when
traveling through the lens-like shape of water on the transparent
member. The scatter increases the cross-sectional area of the
forward laser beam. An increase in the cross-sectional area of the
forward laser beam reduces the resolution of detection of an object
position and the accuracy of detection of an object size.
In general, a given angular region (a given object detectable area
or a given detection area) in front of the body of the vehicle is
scanned by the forward laser beam while the angular direction of
the forward laser beam is sequentially changed among ones separated
at equal unit angles. According to an example, in the absence of a
lens-like shape of water from a surface of the transparent member,
there occur detected echo beams for 5 successive angular directions
of the forward laser beam. On the other hand, in the presence of a
lens-like shape of water on the surface of the transparent member,
there occur detected echo beams for 10 successive angular
directions of the forward laser beam. In this case, a detected
width of an object is equal to twice the actual width thereof.
The previously-mentioned scatter sometimes causes the forward laser
beam to travel out of the detection area in front of the body of
the vehicle. When such a forward laser beam encounters an object
outside the detection area and is reflected thereby, an echo beam
may return to the object recognition apparatus. On the basis of
this echo beam, the apparatus erroneously recognizes the object
outside the detection area as an object therein.
A member having a slit is used to narrow and make the cross section
of a forward laser beam into an ideal shape. Diffraction at the
slit causes an increased intensity of light in a peripheral portion
of the beam, so that the shape of the cross section of the beam
deviates from the ideal one. Therefore, the theoretical shape of
the cross section of the forward laser beam which is used in an
object recognition apparatus differs from the actual shape thereof.
The difference between the theoretical shape and the actual shape
causes a decrease in accuracy of object recognition by the
apparatus.
Japanese patent application publication number P2000-180532A
discloses a method of detecting an object position which is used in
a scanning-type radar for a vehicle. The radar emits a millimeter
wave beam. The method in Japanese application P2000-180532A is
designed to implement the following process. In the case where
there are a plurality of peaks of the power of a reflected beam and
a plurality of mountains formed by the plurality of peaks, and
where reflection due to a side lobe is included in the power of the
reflected beam, a threshold is set to remove the power of the
reflection due to the side lobe so that an angle at a width-wise
center in angles defined by peaks of both ends among the remaining
peaks is detected as a center position of an object.
U.S. Pat. No. 5,627,511 (corresponding to Japanese patent
application publication number 8-122437) discloses a distance
measuring apparatus for an automotive vehicle that compensates for
the influence of particles floating in the air.
The apparatus of U.S. Pat. No. 5,627,511 outputs laser pulse
signals at given angular intervals over an object detectable zone,
and receives a signal produced by reflection of one of the
outputted signals from a reflective object to determine the
distance to the object. The apparatus has the function of
determining a type of the object present in the object detectable
zone. In the case where there are a plurality of signals produced
by dispersion of a single shot of the laser pulse signals, and
where distances derived by signals reflected from most of the
object detectable zone show given shorter distance values, the
object present in the object detectable zone is identified as a
particle such as snow or fog floating in the air.
U.S. Pat. No. 4,699,507 (corresponding to Japanese patent
application publication number 60-201276) discloses an apparatus
and method for measuring the distance to a desired light-reflecting
object. The apparatus and method in U.S. Pat. No. 4,699,507 are
capable of recognizing erroneous measurements due to the presence
of light-reflecting particles suspended in the air. The range of
intensity of reflected light achievable by air-borne particles is
previously stored. When the actual intensity of reflected light
falls within the above-indicated range, the outputting of the
measured distance to the light-reflecting object is inhibited.
U.S. Pat. No. 5,805,527 (corresponding to Japanese patent
application publication number 9-236661) discloses a distance
measuring apparatus which includes a wave transmitting device for
emitting a transmission wave. The apparatus in U.S. Pat. No.
5,805,527 also includes a wave receiving device for receiving a
reflection wave, which results from reflection of the transmission
wave by a reflection object, as a reception wave. A time difference
measuring device is operative for measuring a time difference
between a moment at which the wave transmitting device emits the
transmission wave and a moment at which the wave receiving device
receives the reception wave. A distance calculating device is
operative for calculating a distance to the reflection object on
the basis of the time difference calculated by the time difference
measuring device. An error correcting device is operative for
detecting a time interval during which a signal level of the
reception wave remains higher than a predetermined threshold level,
and for correcting an error in the calculated distance to the
reflection object on the basis of the detected time interval, the
error being caused by a difference in intensity of the reception
wave.
SUMMARY OF THE INVENTION
It is a first object of this invention to provide a method of
accurately recognizing an object.
It is a second object of this invention to provide an apparatus for
accurately recognizing an object.
It is a third object of this invention to provide a recording
medium storing a computer program for accurately recognizing an
object.
A first aspect of this invention provides a method of applying a
transmission wave to a predetermined range in a width-wise
direction of a subject vehicle, and recognizing objects located
ahead of the subject vehicle on the basis of reflected waves which
result from reflections of the transmission wave. The method
comprises the steps of converting the reflected waves into a
received signal; detecting a variation in an intensity of the
received signal along a direction corresponding to the width-wise
direction of the subject vehicle; separating the received signal
into a first signal portion and a second signal portion on the
basis of the detected signal intensity variation, the first signal
portion corresponding to a scattered portion of the transmission
wave, the second signal portion corresponding to an unscattered
portion of the transmission wave; and recognizing objects on the
basis of the second signal portion.
A second aspect of this invention provides an object recognition
apparatus comprising radar means for applying a transmission wave
to a predetermined range in a width-wise direction of a subject
vehicle, converting reflected waves, which result from reflections
of the transmission wave, into a received signal, and detecting
objects on the basis of the received signal; and recognizing means
for recognizing objects located ahead of the subject vehicle on the
basis of results of detection by the radar means. The recognizing
means comprises 1) means for detecting a variation in an intensity
of the received signal along a direction corresponding to the
width-wise direction of the subject vehicle; 2) means for
separating the received signal into a first signal portion and a
second signal portion on the basis of the detected signal intensity
variation, the first signal portion corresponding to a scattered
portion of the transmission wave, the second signal portion
corresponding to an unscattered portion of the transmission wave;
and 3) means for recognizing objects on the basis of the second
signal portion.
A third aspect of this invention is based on the second aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for detecting the intensity of
the received signal, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion on the basis of the detected signal intensity.
A fourth aspect of this invention is based on the third aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for setting a threshold value
equal to a peak value of the detected signal intensity minus a
predetermined value, means for determining whether or not the
detected intensity of the received signal is lower than the
threshold value, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion in response to a result of determining whether or not the
detected intensity of the received signal is lower than the
threshold value.
A fifth aspect of this invention is based on the second aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for calculating a rate of the
detected signal intensity variation, and means for executing the
separation of the received signal into the first signal portion and
the second signal portion in response to the calculated intensity
variation rate.
A sixth aspect of this invention is based on the fifth aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for setting a threshold value
with respect to the calculated intensity variation rate
corresponding to a predetermined steep state, means for determining
whether or not the intensity of the received signal is lower than
the threshold value, and means for executing the separation of the
received signal into the first signal portion and the second signal
portion in response to a result of determining whether or not the
intensity of the received signal is lower than the threshold
value.
A seventh aspect of this invention is based on the fifth aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
An eighth aspect of this invention is based on the fifth aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for, when the calculated
intensity variation rate corresponds to a predetermined gentle and
monotonically-changing state occurring in a prescribed vehicle
width-wise direction position, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
A ninth aspect of this invention is based on the fifth aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for calculating a straight line
approximate to the rate of the detected signal intensity variation
in a least-squares method, means for calculating a slope of the
straight line, and means for calculating the rate of the detected
signal intensity variation from the calculated slope of the
straight line.
A tenth aspect of this invention is based on the second aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for setting a threshold value
with respect to the intensity of the received signal, means for
using the threshold value in the separation of the received signal
into the first signal portion and the second signal portion, and
means for changing the threshold value on the basis of a size of a
recognized object.
An eleventh aspect of this invention is based on the tenth aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises means for continuing the changing of
the threshold value until a length of the recognized object in the
width-wise direction of the subject vehicle falls into a
predetermined range.
A twelfth aspect of this invention is based on the second aspect
thereof, and provides an object recognition apparatus wherein the
received signal contains a pulse, and a time difference between a
leading edge and a trailing edge of the pulse increases as the
intensity of the received signal rises, and wherein the recognizing
means comprises means for estimating the intensity of the received
signal on the basis of the time difference between the leading edge
and the trailing edge of the pulse.
A thirteenth aspect of this invention is based on the second aspect
thereof, and provides an object recognition apparatus wherein the
recognizing means comprises condition estimating means for
estimating whether or not there occurs a scatter condition that the
transmission wave can be scattered, means for, only when the
condition estimating means estimates that there occurs the scatter
condition, executing the separation of the received signal into the
first signal portion and the second signal portion.
A fourteenth aspect of this invention is based on the thirteenth
aspect thereof, and provides an object recognition apparatus
wherein the scatter condition comprises a condition that a
waterdrop can meet a member of the radar means through which the
transmission wave travels.
A fifteenth aspect of this invention is based on the fourteenth
aspect thereof, and provides an object recognition apparatus
wherein the condition estimating means comprises means for
estimating whether or not there occurs the scatter condition on the
basis of whether or not a windshield wiper of the subject vehicle
is active.
A sixteenth aspect of this invention provides a recording medium
storing a program for controlling a computer operating as the
recognizing means in the object recognition apparatus of the second
aspect of this invention.
A seventeenth aspect of this invention provides a method of
applying a transmission wave to a predetermined range in a
width-wise direction of a subject vehicle, and recognizing objects
located ahead of the subject vehicle on the basis of reflected
waves which result from reflections of the transmission wave. The
method comprises the steps of converting the reflected waves into a
received signal; wherein an intensity of a part of the transmission
wave is maximized at a transmission center point, and is decreased
as the part of the transmission wave becomes more distant from the
transmission center point as viewed along the width-wise direction
of the subject vehicle, and wherein a portion of the transmission
wave which has an intensity equal to or higher than a prescribed
intensity is effective for object recognition; detecting a rate of
a variation in an intensity of the received signal along a
direction corresponding to the width-wise direction of the subject
vehicle; separating the received signal into a first signal portion
and a second signal portion on the basis of the detected intensity
variation rate, the first signal portion corresponding to the
portion of the transmission wave which has the intensity equal to
or higher than the prescribed intensity, the second signal portion
corresponding to another portion of the transmission wave; and
recognizing objects on the basis of the first signal portion.
An eighteenth aspect of this invention provides a method of
applying a transmission wave to a predetermined range in a
width-wise direction of a subject vehicle, and recognizing objects
located ahead of the subject vehicle on the basis of reflected
waves which result from reflections of the transmission wave. The
method comprises the steps of converting the reflected waves into a
received signal; wherein an intensity of a part of the transmission
wave is maximized at a transmission center point, and is decreased
as the part of the transmission wave becomes more distant from the
transmission center point as viewed along the width-wise direction
of the subject vehicle, and wherein a portion of the transmission
wave which has an intensity equal to or higher than a prescribed
intensity is effective for object recognition; setting a threshold
value with respect to an intensity of the received signal;
separating the received signal into a first signal portion and a
second signal portion on the basis of the threshold value, the
first signal portion corresponding to the portion of the
transmission wave which has the intensity equal to or higher than
the prescribed intensity, the second signal portion corresponding
to another portion of the transmission wave; recognizing objects on
the basis of the first signal portion; and changing the threshold
value until a length of a recognized object in the width-wise
direction of the subject vehicle falls into a predetermined
range.
A nineteenth aspect of this invention provides an object
recognition apparatus comprising radar means for applying a
transmission wave to a predetermined range in a width-wise
direction of a subject vehicle, converting reflected waves, which
result from reflections of the transmission wave, into a received
signal, and detecting objects on the basis of the received signal;
and recognizing means for recognizing objects located ahead of the
subject vehicle on the basis of results of detection by the radar
means; wherein an intensity of a part of the transmission wave is
maximized at a transmission center point, and is decreased as the
part of the transmission wave becomes more distant from the
transmission center point as viewed along the width-wise direction
of the subject vehicle, and wherein a portion of the transmission
wave which has an intensity equal to or higher than a prescribed
intensity is effective for object recognition. The recognizing
means comprises 1) means for detecting a rate of a variation in an
intensity of the received signal along a direction corresponding to
the width-wise direction of the subject vehicle; 2) means for
separating the received signal into a first signal portion and a
second signal portion on the basis of the detected intensity
variation rate, the first signal portion corresponding to the
portion of the transmission wave which has the intensity equal to
or higher than the prescribed intensity, the second signal portion
corresponding to another portion of the transmission wave; and 3)
means for recognizing objects on the basis of the first signal
portion.
A twentieth aspect of this invention is based on the nineteenth
aspect thereof, and provides an object recognition apparatus
wherein the recognizing means comprises means for setting a
threshold value with respect to the calculated intensity variation
rate corresponding to a predetermined steep state, means for
determining whether or not the intensity of the received signal is
lower than the threshold value, and means for executing the
separation of the received signal into the first signal portion and
the second signal portion in response to a result of determining
whether or not the intensity of the received signal is lower than
the threshold value.
A twenty-first aspect of this invention is based on the nineteenth
aspect thereof, and provides an object recognition apparatus
wherein the recognizing means comprises means for, when the
calculated intensity variation rate corresponds to a predetermined
gentle and monotonically-changing state, judging that a
corresponding recognized object exists outside a predetermined
recognition area.
A twenty-second aspect of this invention is based on the nineteenth
aspect thereof, and provides an object recognition apparatus
wherein the recognizing means comprises means for, when the
calculated intensity variation rate corresponds to a predetermined
gentle and monotonically-changing state occurring in a prescribed
vehicle width-wise direction position, judging that a corresponding
recognized object exists outside a predetermined recognition
area.
A twenty-third aspect of this invention is based on the nineteenth
aspect thereof, and provides an object recognition apparatus
wherein the recognizing means comprises means for calculating a
straight line approximate to the rate of the detected signal
intensity variation in a least-squares method, means for
calculating a slope of the straight line, and means for calculating
the rate of the detected signal intensity variation from the
calculated slope of the straight line.
A twenty-fourth aspect of this invention provides an object
recognition apparatus comprising radar means for applying a
transmission wave to a predetermined range in a width-wise
direction of a subject vehicle, converting reflected waves, which
result from reflections of the transmission wave, into a received
signal, and detecting objects on the basis of the received signal;
and recognizing means for recognizing objects located ahead of the
subject vehicle on the basis of results of detection by the radar
means; wherein an intensity of a part of the transmission wave is
maximized at a transmission center point, and is decreased as the
part of the transmission wave becomes more distant from the
transmission center point as viewed along the width-wise direction
of the subject vehicle, and wherein a portion of the transmission
wave which has an intensity equal to or higher than a prescribed
intensity is effective for object recognition. The recognizing
means comprises 1) means for setting a threshold value with respect
to an intensity of the received signal; 2) means for separating the
received signal into a first signal portion and a second signal
portion on the basis of the threshold value, the first signal
portion corresponding to the portion of the transmission wave which
has the intensity equal to or higher than the prescribed intensity,
the second signal portion corresponding to another portion of the
transmission wave; 3) means for recognizing objects on the basis of
the first signal portion; and 4) means for changing the threshold
value until a length of a recognized object in the width-wise
direction of the subject vehicle falls into a predetermined
range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a vehicle control apparatus according
to a first embodiment of this invention.
FIG. 2 is a diagram of a laser radar sensor in FIG. 1.
FIG. 3 is a diagram of a first example of the time-domain variation
in the voltage of the output signal from an amplifier in FIG.
2.
FIG. 4 is a diagram of a second example of the time-domain
variation in the voltage of the output signal from the amplifier in
FIG. 12.
FIG. 5 is an operation flow diagram of an electronic control unit
(ECU) in FIG. 1.
FIG. 6 is a flowchart of a portion of a program for the ECU in FIG.
1.
FIG. 7 is a diagram of an example of detected point-like object
parts, and segments which result from unifying close ones of the
detected point-like object parts.
FIG. 8 is a diagram of conversion of coordinates.
FIG. 9 is a diagram of a detection area scanned by the laser radar
sensor in FIG. 1, and preceding vehicles in the detection area.
FIG. 10 is a diagram of an excessively low threshold value, and a
first example of the relation between an echo pulse width and a
beam order number.
FIG. 11 is a diagram of the excessively low threshold value and a
proper threshold value, and the first example of the relation
between the echo pulse width and the beam order number.
FIG. 12 is a diagram of a second example of the relation between
the echo pulse width and the beam order number.
FIG. 13 is a flowchart of a block in FIG. 6.
FIG. 14 is a diagram of the second example of the relation between
the echo pulse width and the beam order number.
FIG. 15 is a diagram of a third example of the relation between the
echo pulse width and the beam order number.
FIG. 16 is a diagram of a fourth example of the relation between
the echo pulse width and the beam order number.
FIG. 17 is a diagram of a fifth example of the relation between the
echo pulse width and the beam order number.
FIG. 18 is a diagram of a sixth example of the relation between the
echo pulse width and the beam order number.
FIG. 19 is a diagram of a seventh example of the relation between
the echo pulse width and the beam order number.
FIG. 20 is a diagram of an eighth example of the relation between
the echo pulse width and the beam order number.
FIG. 21 is a diagram of a ninth example of the relation between the
echo pulse width and the beam order number.
FIG. 22 is a diagram of a tenth example of the relation between the
echo pulse width and the beam order number.
FIG. 23 is a diagram of an eleventh example of the relation between
the echo pulse width and the beam order number.
FIG. 24 is a flowchart of a portion of a program for an ECU in a
second embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
FIG. 1 shows a vehicle control apparatus according to a first
embodiment of this invention. The vehicle control apparatus is
mounted on a vehicle which will be referred to as the present
vehicle or the subject vehicle. The vehicle control apparatus
alarms when an obstacle in a specified condition exists in a given
angular region (a given detection area) in front of the present
vehicle. The vehicle control apparatus adjusts the speed of the
present vehicle in accordance with the speed of a preceding
vehicle. The vehicle control apparatus includes a recording
medium.
As shown in FIG. 1, the vehicle control apparatus includes an
electronic control unit (ECU) 3 having a computer such as a
microcomputer. The computer in the ECU 3 has a combination of an
input/output (I/O) interface, a CPU, a ROM, and a RAM. The ECU 3
(the computer therein) operates in accordance with a program stored
in the ROM. The program may be stored in the RAM. In this case, the
RAM is provided with a backup device.
Alternatively, the program may be stored in a recording medium such
as a floppy disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a
hard disk. In this case, the ECU 3 is connected with a drive for
the recording medium, and the program is downloaded into the
computer of the ECU 3 through the drive.
The vehicle control apparatus includes a laser radar sensor 5, a
vehicle speed sensor 7, a brake switch 9, and a throttle opening
degree sensor (a throttle position sensor) 11 which are connected
to the ECU 3. The output signals of the devices 5, 7, 9, and 11 are
inputted into the ECU 3.
The vehicle control apparatus includes an alarm sound generator 13,
a distance indicator 15, a sensor failure indicator 17, a brake
drive device 19, a throttle drive device 21, and an automotive
automatic transmission control device 23 which are connected to the
ECU 3. The ECU 3 outputs drive signals to the devices 13, 15, 17,
19, 21, and 23.
The vehicle control apparatus includes an alarm sound volume
setting device 24, an alarm sensitivity setting device 25, a cruise
control switch 26, a steering sensor 27, a yaw rate sensor 28, and
a windshield wiper switch 30 which are connected to the ECU 3. The
output signals of the devices 24, 25, 26, 27, 28, and 30 are
inputted into the ECU 3. The alarm sound volume setting device 24
acts to set the volume of alarm sound. The alarm sensitivity
setting device 25 acts to set the sensitivity in a warning
determination process mentioned later.
The vehicle control apparatus includes a power supply switch 29
connected to the ECU 3. When the power supply switch 29 is changed
to its on position, the ECU 3 is powered and starts predetermined
processes.
As shown in FIG. 2, the laser radar sensor 5 contains a light
emitting portion 5A, a light receiving portion 5B, and a CPU
70.
The CPU 70 includes a memory storing a program. The CPU 70 operates
in accordance with the program.
The light emitting portion 5A in the laser radar sensor 5 includes
a lens 71, a scanner 72, a motor drive circuit 74, a semiconductor
laser diode 75, a laser-diode drive circuit 76, and a glass plate
77. The scanner 72 has a mirror 73 and a motor (not shown). The
mirror 73 is mechanically connected with the output shaft of the
motor. The mirror 73 can be rotated by the motor. The motor is
electrically connected to the motor drive circuit 74. The motor
drive circuit 74 is connected to the CPU 70. The laser diode 75 is
connected to the laser-diode drive circuit 76. The laser-diode
drive circuit 76 is connected to the CPU 70.
The laser-diode drive circuit 76 receives a laser-diode drive
signal from the CPU 70. The laser-diode drive circuit 76 activates
the laser diode 75 in response to the laser-diode drive signal so
that the laser diode 75 emits a pulse laser beam. The emitted pulse
laser beam travels through the lens 71 before reaching the mirror
73 and being reflected thereby. The reflection-resultant pulse
laser beam propagates through the glass plate 77 before being
outputted from the light emitting portion 5A as a forward laser
beam. In the case where a waterdrop or a raindrop encounters the
glass plate 77 and changes into a lens-like shape thereon, the
forward laser beam may be scattered while traveling through the
lens-like shape of water on the glass plate 77.
The motor drive circuit 74 receives a motor drive signal from the
CPU 70. The motor drive circuit 74 activates the motor in response
to the motor drive signal so that the motor periodically and
cyclically rotates the mirror 73 along clockwise and
counterclockwise directions in a predetermined limited angular
range. The periodical and cyclical rotation of the mirror 73 causes
periodical and cyclical deflection of the forward laser beam,
thereby enabling a given angular region in front of the present
vehicle to be periodically scanned by the forward laser beam. The
given angular region corresponds to a given sectorial detection
area monitored by the laser radar sensor 5.
During every scanning period (every frame period), the angular
direction of the forward laser beam is changed a unit-angle by a
unit-angle. The unit angle corresponds to, for example, 0.15
degrees. The detection area (the given angular region) scanned by
the forward laser beam has an angular range of, for example, about
16 degrees which extends in the width-wise direction of the present
vehicle as viewed therefrom. In this case, the detection area
corresponds to 105 image points or pixels (105 multiplied by 0.15
degrees equals about 16 degrees) composing one frame. The forward
laser beams in the respective 105 angular directions are serially
numbered from "0" to "104". The forward laser beam numbered "0" is
in the leftmost direction corresponding to an angle of about -7.8
degrees. The forward laser beam numbered "104" is in the rightmost
direction corresponding to an angle of about +7.8 degrees. These
numbers "0" to "104" are referred to as beam order numbers. The 105
image points or pixels composing one frame are identified by the
beam order numbers "0" to "104" respectively.
The light receiving portion 5B in the laser radar sensor 5 includes
a lens 81 and a light receiving element 83. The light receiving
element 83 contains, for example, a photodiode or a photodetector.
The light receiving element 83 is connected to an amplifier 85. The
amplifier 85 is connected to a comparator 87. The comparator 87 is
connected to a time measurement circuit 89. The time measurement
circuit 89 is connected to the CPU 70.
In the case where an object exists in the detection area (the given
angular region), the forward laser beam encounters the object
before being at least partially reflected thereby. A portion of the
reflected laser beam returns to the laser radar sensor 5 as an echo
laser beam. Specifically, the echo laser beam travels through the
lens 81 before being incident to the light receiving element 83.
The light receiving element 83 converts the echo laser beam into a
corresponding electric signal (referred to as an echo signal). The
light receiving element 83 outputs the electric signal to the
amplifier 85. The device 85 amplifies the output signal of the
light receiving element 83. The amplifier 85 outputs the
amplification-resultant signal to the comparator 87. The device 87
compares the output signal of the amplifier 85 with a predetermined
reference voltage (a predetermined threshold voltage) Vth, thereby
converting the output signal of the amplifier 85 into a binary
signal or a pulse signal. The comparator 87 outputs the binary
signal (the pulse signal) to the time measurement circuit 89.
The time measurement circuit 89 receives the laser-diode drive
signal from the CPU 70. Every pulse in the laser-diode drive signal
corresponds to a pulse of the forward laser beam. The time
measurement circuit 89 responds to every pulse in the laser-diode
drive signal. In the presence of a detected object in the detection
area, the output signal of the comparator 87 has a pulse caused by
a pulse echo laser beam corresponding to a pulse of the forward
laser beam. The width of the pulse in the output signal of the
comparator 87 increases as the intensity of the pulse echo laser
beam rises or the intensity of the echo signal rises. The time
measurement circuit 89 responds to every pulse in the output signal
of the comparator 87. Specifically, the time measurement circuit 89
uses every pulse in the laser-diode drive signal as a start pulse
PA. The time measurement circuit 89 uses the corresponding pulse in
the output signal of the comparator 87 as a stop pulse PB. The time
measurement circuit 89 measures the phase difference between the
start pulse PA and the stop pulse PB, that is, the time interval or
the time difference between the moment of the occurrence of the
start pulse PA and the moment of the occurrence of the stop pulse
PB. The time measurement circuit 89 generates a digital signal
representing the measured phase difference (the measured time
interval or difference). The time measurement circuit 89 outputs
the time-interval-representing digital signal to the CPU 70. In
addition, the time measurement circuit 89 measures the width of the
stop pulse PB as an indication of the intensity of the related
pulse echo laser beam. The time measurement circuit 89 generates a
digital signal representing the measured pulse width (the measured
echo intensity). The time measurement circuit 89 outputs the
pulse-width-representing digital signal to the CPU 70.
The CPU 70 generates measurement data in response to the
time-interval-representing digital signal and the
pulse-width-representing digital signal. The measurement data
represents the angle or the angular position ".theta." of an object
in the detection area, the distance "r" to the object from the
present vehicle, and the width of the related pulse in the output
signal of the comparator 87 (that is, the intensity of the related
echo laser beam or the related echo signal). The CPU 70 outputs the
measurement data to the ECU 3.
In general, since the object is greater than the cross-sectional
area of the forward laser beam and is scanned thereby, the
measurement data corresponding to one forward-laser-beam angular
direction relates to a partial object or a point-like part of an
object. Objects detected by the laser radar sensor 5 include
obstacles with respect to the present vehicle.
The amplifier 85 uses a bipolar transistor. The amplifier 85 is
saturated when the level of an input signal thereinto exceeds a
certain value. FIG. 3 shows an example of a variation in the output
signal of the amplifier 85 which occurs while the level of the
output signal of the light receiving element 83 (that is, the
intensity of the echo laser beam) remains below the certain value.
As shown in FIG. 3, the amplifier 85 is not saturated under such a
condition. FIG. 4 shows an example of a variation in the output
signal of the amplifier 85 which occurs during a time interval
including a portion where the level of the output signal of the
light receiving element 83 (that is, the intensity of the echo
laser beam) increases above the certain value. As shown in FIG. 4,
the amplifier 85 is saturated under such a condition. Specifically,
the level of the output signal of the amplifier 85 continues to be
fixed at a saturation value Vsat while the level of the output
signal of the light receiving element 83 remains above the certain
value. According to the minority carrier storage effect, the
trailing edge of a pulse in the output signal of the light
receiving element 83 is delayed as the intensity of an echo laser
beam rises (see the two-dot dash curve in FIG. 4). The width of a
pulse in the output signal of the comparator 87 corresponds to the
time interval during which the voltage of the output signal of the
amplifier 85 remains higher than the predetermined reference
voltage Vth. The width of a pulse in the output signal of the
comparator 87 depends on the intensity of an echo laser beam or an
echo signal. Specifically, the width of a pulse is approximately
proportional to the logarithm of the intensity of an echo laser
beam or an echo signal. Accordingly, it is possible to estimate the
intensity of an echo laser beam or an echo signal from the width of
a pulse.
The laser beam may be replaced by a radio wave beam, a millimeter
wave beam, or an ultrasonic beam. The scanning may be implemented
by controlling the echo beam reception by the laser radar sensor
5.
The ECU 3 receives the measurement data from the laser radar sensor
5. The ECU 3 recognizes objects on the basis of the measurement
data. The ECU 3 detects a preceding vehicle with respect to the
present vehicle on the basis of the result of the object
recognition. In addition, the ECU 3 detects conditions of the
preceding vehicle. The ECU 3 executes inter-vehicle distance
control. During the execution of the inter-vehicle distance
control, the ECU 3 generates and outputs suitable drive signals to
the brake drive unit 19, the throttle drive device 21, and the
automotive automatic transmission control device 23 to adjust the
speed of the present vehicle in accordance with the conditions of
the preceding vehicle. Simultaneously with the execution of the
inter-vehicle distance control, the ECU 3 executes a warning
determination process designed to generate an alarm in the case
where an obstacle corresponding to a recognized object remains in a
specified area during longer than a prescribed time interval. The
obstacle corresponds to, for example, a preceding vehicle, a
stationary vehicle, a guardrail on a road side, or a prop on a road
side.
The vehicle speed sensor 7 is associated with a wheel of the
present vehicle. The vehicle speed sensor 7 detects the rotational
speed of the vehicle wheel. The vehicle speed sensor 7 outputs a
signal to the ECU 3 which represents the detected rotational speed
of the vehicle wheel.
The steering sensor 27 detects the degree of operation of a vehicle
steering wheel (not shown), that is, the steering angle in the
present vehicle. Specifically, the steering sensor 27 detects a
quantity of change of the steering angle. The steering sensor 27
outputs a signal to the ECU 3 which represents the detected
quantity of change of the steering angle. When the power supply
switch 29 is moved to its on position, a variable used in the ECU 3
as an indication of a detected steering angle (radian) is
initialized to "0". After the movement of the power supply switch
29 to its on position, the detected steering angle is decided by
integrating the quantity of change of the steering angle which is
represented by the output signal of the steering sensor 27.
The yaw rate sensor 28 detects the rate .OMEGA. (radian/second) of
change in the rotational angle (the yaw angle) of the body of the
present vehicle about the vertical axis thereof. The yaw rate
sensor 28 informs the ECU 3 of the detected yaw rate .OMEGA..
When the cruise control switch 26 is changed to its on position,
the ECU 3 operates to start the vehicle cruise control. During the
execution of the vehicle cruise control, signal processing for the
inter-vehicle distance control can be implemented by the ECU 3.
When the ECU 3 determines that the present vehicle is excessively
close to an objective preceding vehicle, the alarm sound generator
13 is activated by the ECU 3 to generate alarm sound. The volume of
the generated alarm sound is equalized to a level adjustably
determined by the alarm sound volume setting device 24. The
sensitivity of generation of alarm sound can be adjusted by the
alarm sensitivity setting device 25.
The brake switch 9 detects depression of a brake pedal of the
present vehicle. The brake switch 9 informs the ECU 3 of the
detected brake-pedal depression. The ECU 3 generates a drive signal
for the brake drive device 19 in response to information containing
the information of the detected brake-pedal depression.
The ECU 3 outputs the generated drive signal to the brake drive
device 19. The brake drive device 19 adjusts the braking pressure
in response to the drive signal outputted from the ECU 3.
The throttle opening degree sensor 11 detects the degree of opening
through a throttle valve in an engine for driving the present
vehicle. The throttle opening degree sensor 11 outputs a signal to
the ECU 3 which represents the detected throttle opening degree.
The ECU 3 controls the throttle drive device 21 in response to the
detected throttle opening degree, thereby adjusting the actual
degree of opening through the throttle valve and adjusting the
power output of the engine.
The ECU 3 determines whether or not the laser radar sensor 5 is
operating normally by referring to the output signal therefrom.
When the ECU 3 determines that the laser radar sensor 5 is not
operating normally, the sensor failure indicator 17 is controlled
by the ECU 3 to indicate a failure.
The ECU 3 selects an objective preceding vehicle from among
candidate preceding vehicles detected in response to the output
signal of the laser radar sensor 5. The ECU 3 calculates the
distance to the objective preceding vehicle from the present
vehicle. The distance indicator 15 is controlled by the ECU 3 to
indicate the calculated distance to the objective preceding vehicle
from the present vehicle.
The automotive automatic transmission control device 23 selects a
used gear position of an automotive automatic transmission and
thereby controls the speed of the present vehicle in response to
the output signal from the ECU 3.
A windshield wiper of the present vehicle is activated and
deactivated when the windshield wiper switch 30 is changed between
an on position and an off position. The windshield wiper switch 30
outputs a signal to the ECU 3 which represents whether the
windshield wiper switch 30 is in its on position or its off
position, that is, whether the windshield wiper is activated or
deactivated.
FIG. 5 shows the flow of operation of the ECU 3 rather than the
hardware structure thereof. With reference to FIG. 5, an object
recognition block 43 receives, from the CPU 70 in the laser radar
sensor 5, measurement data representing a distance "r" and an angle
".theta." concerning each detected object (each detected partial
object or each detected point-like object part). The object
recognition block 43 converts the distance and angle data of polar
coordinates into measurement data of X-Z orthogonal coordinates
designed so that the origin (0, 0) coincides with the center of a
laser radar formed by the sensor 5, and the X axis and the Z axis
coincide with a width-wise direction and a longitudinal forward
direction of the present vehicle respectively. The object
recognition block 43 groups detected partial objects (detected
point-like object parts) represented by the orthogonal-coordinate
measurement data into sets or segments corresponding to detected
complete objects respectively. The grouping and the segments will
be described later. Pieces of the grouping-resultant segment data
which indicate respective segments are object-unit data pieces
(per-object data pieces). A model of a complete object which is
represented by central position data, size data, relative-speed
data, and stationary-moving determination result data (recognition
type data) will be called a target model.
A vehicle speed calculation block 47 computes the speed V of the
present vehicle on the basis of the output signal from the vehicle
speed sensor 7.
The object recognition block 43 calculates the central position (X,
Z) and size (W, D) of each detected complete object on the basis of
the grouping-resultant segment data. Here, W denotes a transverse
width, and D denotes a depth. The object recognition block 43
calculates the speed (Vx, Vz) of the complete object relative to
the present vehicle from a time-domain variation in the central
position (X, Z) thereof. The object recognition block 43 is
informed of the speed V of the present vehicle by the vehicle speed
calculation block 47. The object recognition block 43 determines
whether or not each detected complete object is stationary or
moving on the basis of the vehicle speed V and the relative speed
(Vx, Vz). The object recognition block 43 informs a
preceding-vehicle determination block 53 of the central position,
the size, the relative speed, and the recognition type (the
stationary-moving determination result) of each detected complete
object.
The measurement data fed to the object recognition block 43 from
the CPU 70 in the laser radar sensor 5 also represent an echo
intensity (an echo pulse width) concerning each detected object
(each detected partial object or each detected point-like object
part). The object recognition block 43 corrects or revises the
segment data in response to the echo intensities (the echo pulse
widths) through a data separation process for removing
scatter-caused data components or scatter-caused data portions.
A sensor failure detection block 44 receives the output data (the
object-recognition result data) from the object recognition block
43 which represent the object parameters calculated thereby. The
sensor failure detection block 44 determines whether the output
data from the object recognition block 43 are in a normal range or
an abnormal range. When the output data from the object recognition
block 43 are in the abnormal range, the sensor failure detection
block 44 activates the sensor failure indicator 17 to indicate a
failure.
A steering angle calculation block 49 computes the steering angle
regarding the present vehicle on the basis of the output signal
from the steering sensor 27. A yaw rate calculation block 51
computes the yaw rate of the present vehicle on the basis of the
output signal from the yaw rate sensor 28.
A curvature-radius calculation block 57 is informed of the vehicle
speed V by the vehicle speed calculation block 47. The
curvature-radius calculation block 57 is informed of the computed
steering angle by the steering angle calculation block 49. The
curvature-radius calculation block 57 is informed of the computed
yaw rate by the yaw rate calculation block 51. On the basis of the
vehicle speed V, the steering angle, and the yaw rate, the
curvature-radius calculation block 57 computes the radius R of
curvature of the road along which the present vehicle is traveling.
The curvature-radius calculation block 57 informs the
preceding-vehicle determination block 53 of the computed curvature
radius R.
The preceding-vehicle determination block 53 selects an objective
preceding vehicle among the detected complete objects on the basis
of the central positions, the sizes, the relative speeds, and the
recognition types thereof, and on the basis of the curvature radius
R. The preceding-vehicle determination block 53 gets information of
the distance Z to the objective preceding vehicle and also
information of the relative speed Vz of the objective preceding
vehicle. The preceding-vehicle determination block 53 feeds an
inter-vehicle distance control and warning determination block 55
with the information of the distance Z to the objective preceding
vehicle and the information of the relative speed Vz of the
objective preceding vehicle.
The inter-vehicle distance control and warning determination block
55 is informed of the vehicle speed V by the vehicle speed
calculation block 47. The inter-vehicle distance control and
warning determination block 55 detects setting conditions of the
cruise control switch 26 from the output signal thereof. The
inter-vehicle distance control and warning determination block 55
detects the state of the brake switch 9 from the output signal
thereof. The state of the brake switch 9 represents whether or not
the vehicle brake pedal is depressed. The inter-vehicle distance
control and warning determination block 55 is informed of the
degree of opening through the engine throttle valve by the throttle
opening degree sensor 11. The inter-vehicle distance control and
warning determination block 55 is informed of the alarm volume
setting value by the alarm sound volume setting device 24. The
inter-vehicle distance control and warning determination block 55
is informed of the alarm sensitivity setting value by the alarm
sensitivity setting device 25. The inter-vehicle distance control
and warning determination block 55 implements a warning
determination and a cruise determination in response to the
distance Z to the objective preceding vehicle, the relative speed
Vz of the objective preceding vehicle, the vehicle speed V, the
setting conditions of the cruise control switch 26, the state of
the brake switch 9, the throttle opening degree, and the alarm
sensitivity setting value. During the warning determination, the
inter-vehicle distance control and warning determination block 55
determines whether or not an alarm should be generated. During the
cruise determination, the inter-vehicle distance control and
warning determination block 55 determines the contents of vehicle
speed control. When it is determined that an alarm should be
generated, the inter-vehicle distance control and warning
determination block 55 outputs an alarm generation signal to the
alarm sound generator 13. In this case, the alarm sound generator
13 produces alarm sound. The inter-vehicle distance control and
warning determination block 55 adjusts the level of the alarm sound
in accordance with the sound volume set by the alarm sound volume
setting device 24. In the case where the cruise determination
corresponds to the execution of cruise control, the inter-vehicle
distance control and warning determination block 55 outputs
suitable control signals to the automotive automatic transmission
control device 23, the brake drive device 19, and the throttle
drive device 21. During the execution of the warning control and
the cruise control, the inter-vehicle distance control and warning
determination block 55 outputs an indication signal to the distance
indicator 15 to inform the vehicle's driver of distance-related
conditions. For example, the device 15 indicates the distance Z to
the objective preceding vehicle.
As shown in FIG. 5, the output signal of the windshield wiper
switch 30 is fed to the object recognition block 43 and the
inter-vehicle distance control and warning determination block 55.
The output signal of the windshield wiper switch 30 is used by the
object recognition block 43 and the inter-vehicle distance control
and warning determination block 55. The execution of the data
separation process by the object recognition block 43 is
selectively permitted and inhibited in response to the output
signal of the windshield wiper switch 30.
As previously mentioned, the ECU 3 operates in accordance with a
program stored in its internal ROM or RAM. FIG. 6 is a flowchart of
a portion of the program for the ECU 3 which relates to object
recognition. The program portion in FIG. 6 is repetitively executed
at a period corresponding to the period of the scanning implemented
by the laser radar sensor 5.
As shown in FIG. 6, a first step S10 of the program portion
receives distance and angle measurement data, and echo-pulse-width
data (echo intensity data) from the laser radar sensor 5 for one
period of the scanning. In other words, the step S10 receives
distance and angle measurement data, and echo-pulse-width data
(echo intensity data) corresponding to one frame. The scanning
period is equal to, for example, 100 msec.
A step S20 following the step S10 deletes components from the
distance and angle data which correspond to signal intensities
(echo intensities or echo pulse widths) lower than a threshold
value "A", and which correspond to distances shorter than an
effective distance. The threshold value "A" and the effective
distance are set by a step S40 (mentioned later) at the
immediately-previous execution cycle of the program portion.
A step S30 subsequent to the step S20 processes the undeleted
distance and angle data. Specifically, the step S30 converts the
undeleted distance and angle data of polar coordinates into
measurement data of X-Z orthogonal coordinates. The
orthogonal-coordinate measurement data represent detected partial
objects or detected point-like object parts. The step S30 groups
the detected point-like object parts (the detected partial objects)
into segments corresponding to detected complete objects
respectively.
With reference to FIG. 7, the step S30 searches the detected
point-like object parts for close ones which are spaced by
X-axis-direction distances .DELTA.X of 0.2 m or less and
Z-axis-direction distances .DELTA.Z of 2 m or less. The step S30
combines or unifies the close point-like object parts into a
segment (a set) corresponding to a detected complete object. There
can be a plurality of segments. The step S30 generates data
representing segments which are referred to as segment data.
Specifically, one segment data piece (one data piece representing a
segment) generated by the step S30 corresponds to a rectangular
region having two sides parallel to the X axis and two sides
parallel to the Z axis. One segment data piece contains an
information piece indicating the central position of the related
segment, an information piece indicating the size (W, D) of the
segment, an information piece indicating the beam order number
corresponding to the left-hand edge of the segment, and an
information piece indicating the beam order number corresponding to
the right-hand edge of the segment.
A step S40 following the step S30 controls the threshold value "A"
and the effective distance for the step S20. The control-resultant
threshold value "A" and the control-resultant effective distance
are used by the step S20 at the next execution cycle of the program
portion. In the case where segments represented by the data
generated by the step S30 include a segment having a transverse
width greater than a predetermined value (equal to, for example,
2.6 m), the step S40 increments the threshold value "A" for every
scanning period until the transverse width of the segment of
interest decreases below the predetermined value. The incremented
threshold value "A" is used by the step S20 at the next execution
cycle of the program portion. Preferably, the predetermined value
is slightly greater than the maximum among the widths of ordinary
trucks. The predetermined value is equal to, for example, 2.5 m. It
is thought that a segment having a transverse width greater than
the predetermined value is caused by the scatter of a laser beam
which apparently increases an object image size.
Since signal intensities (echo intensities) are represented by
pulse widths, the threshold value "A" controlled by the step S40
and used by the step S20 corresponds to one referred as a
pulse-width threshold value. The details of the control of the
threshold value "A" and the effective distance by the step S40 are
as follows.
1 In the case where segments represented by the data generated by
the step S30 include a segment having a transverse width greater
than 2.6 m and having a mean pulse width greater than the
pulse-width threshold value, the step S40 increments the
pulse-width threshold value by 1 LSB (corresponding to 6.4
nsec).
The pulse-width threshold value is variable only in the range of 10
to 20 LSB's. In addition, the step S40 sets the effective distance
equal to the distance to the segment of interest plus 5 m.
2 In the case where a segment having a transverse width greater
than 2.6 m and having a mean pulse width greater than the
pulse-width threshold value is absent from segments represented by
the data generated by the step S30, the step S40 decrements the
pulse-width threshold value by 1 LSB. In addition, the step S40
sets the effective distance equal to the distance to the segment of
interest minus -0.5 m. The lower limit of the effective distance is
equal to 35 m.
3 In the case where segments represented by the data generated by
the step S30 include a segment located at a distance shorter than
the distance of a segment satisfying the previously-mentioned
conditions 1, and where the shorter-distance segment has a mean
pulse width smaller than the pulse-width threshold value and has a
straight-road conversion-resultant X coordinate whose absolute
value is smaller than 1.0 m, the step S40 sets the pulse-width
threshold value to a predetermined initial value (equal to, for
example, 10 LSB's). In addition, the step S40 sets the effective
distance to a predetermined initial value (equal to, for example,
35 m).
The above-mentioned conditions 2 prevent the step S20 from deleting
preceding-vehicle-corresponding components of the distance and
angle data. The straight-road conversion-resultant X coordinate
will be explained below. Specifically, as shown in FIG. 8, the step
S40 converts the coordinates (Xo, Zo) of the central position and
the transverse width Wo of each complete object (each target model)
into the coordinates (X, Z) and the transverse width W thereof
which occur on the assumption that the present vehicle is traveling
along a straight road. In more detail, the step S40 converts the
coordinate values Xo and Zo and the transverse width Wo into the
coordinate values X and Z and the transverse width W according to
the following equations.
where R denotes the road curvature radius. The sign of the road
curvature radius R is positive for a right-hand curve, and is
negative for a left-hand curve. The equations (1), (2), and (3) are
made on the basis of approximation using the assumption that the
absolute value of the coordinate value Xo is significantly smaller
than the road curvature radius R and the coordinate value Zo
(.vertline.Xo.vertline.<<.vertline.R.vertline. and
.vertline.Xo.vertline.<<Z). In the case where the laser radar
sensor 5 is significantly distant from the center of the body of
the present vehicle, the X-Z coordinate system is corrected so that
the origin thereof will coincide with the vehicle center.
The control of the threshold value "A" and the effective distance
by the step S40 provides an advantage as follows. It is assumed
that as shown in FIG. 9, two abreast vehicles located ahead of the
present vehicle exist in the detection area monitored by the laser
radar sensor 5. In this case, as shown in FIG. 10, the echo
intensity (the echo pulse width) varies in accordance with the beam
order number. There are four peaks in the echo intensity which
correspond to the four reflectors of the two preceding vehicles.
There is a valley in the echo intensity between the second leftmost
peak and the second rightmost peak. When the threshold value "A" is
lower than the valley between the second leftmost peak and the
second rightmost peak as shown in FIG. 10, the two preceding
vehicles are recognized as a single object having a transverse
width slightly greater than the length between the leftmost peak
and the rightmost peak. The transverse width of the recognized
object is equal to the sum of the transverse widths of the two
preceding vehicles and the transverse spacing therebetween.
Therefore, the transverse width of the recognized object is greater
than 2.6 m. Thus, the previously-mentioned conditions 1 occur. As a
result, the threshold value "A" is periodically incremented on a
stepwise basis until the transverse width of a recognized object or
the transverse widths of recognized objects decrease below 2.6 m.
During this stage, when the threshold value "A" is greater than the
valley between the second leftmost peak and the second rightmost
peak, the two preceding vehicles are recognized as two separate
objects. When the threshold value "A" is increased to a suitable
value as shown in FIG. 11, the transverse widths of the two
recognized objects are smaller than 2.6 m.
With reference back to FIG. 6, a step S50 follows the step S40.
The step S50 refers to the output signal of the windshield wiper
switch 30, and thereby determines whether or not the switch 30 is
in its on position. When the windshield wiper switch 30 is in its
on position, the program advances from the step S50 to a data
separation block (an anti-scatter block) S60. Otherwise, the
program jumps from the step S50 to a step S70.
The data separation block S60 implements signal processing for data
separation corresponding to anti-scatter. The data separation block
S60 processes the segment data pieces provided by the step S30 into
processing-resultant segment data pieces. After the data separation
block S60, the program advances to the step S70.
The step S70 generates target models from the segment data pieces
provided by the step S30 or the data separation block S60. After
the step S70, the current execution cycle of the program portion
ends.
Signal processing implemented by the data separation block S60 is
as follows. The data separation block S60 separates the 1-frame
echo signal into components caused by scattered forward laser beams
and components caused by unscattered forward laser beams in
response to a variation in the intensity of the echo signal along
the width-wise direction of the present vehicle. Generally, a
scattered forward laser beam occurs when an original forward laser
beam travels through a lens-like shape of water on the glass plate
77 in the laser radar sensor 5. The data separation block S60
discards the scatter-caused signal components and enables only the
scatter-unrelated signal components to be used in the object
recognition (the target-model generation) by the step S70.
Attention have been paid to the following two features A1 and A2.
A1 The intensities of scatter-unrelated signal components are
greater than those of scatter-caused signal components by a factor
of more than 100 (that is, by two orders or more).
A2 variation in the intensities of scatter-unrelated signal
components along the width-wise direction of the present vehicle
has a steep rising edge while that of scatter-caused signal
components has a gentle rising edge.
The data separation block S60 implements a discrimination between
scatter-unrelated signal components and scatter-caused signal
components on the basis of the above-mentioned features A1 and A2
As previously mentioned, the width of a pulse in the output signal
of the comparator 87 depends on the intensity of an echo laser beam
(that is, the intensity of an echo signal). Specifically, the width
of a pulse is approximately proportional to the logarithm of the
intensity of an echo laser beam or an echo signal. Accordingly, it
is possible to estimate the intensity of an echo laser beam or an
echo signal from the width of a pulse. The data separation block
S60 uses the pulse width as an indication of the echo
intensity.
With reference to FIG. 12, the data separation block S60 refers to
the 1-frame measurement data and thereby plots values of the echo
pulse width as a function of the beam order number. In FIG. 12, the
ordinate is assigned to the echo pulse width while the abscissa is
assigned to the beam order number. A threshold value "B" is set
equal to the maximum among the values of the echo pulse width minus
a predetermined value. The threshold value "B" is indicated in FIG.
12 as a horizontal line. The graphic points in FIG. 12 which
correspond to the respective values of the echo pulse width are
connected by a line (referred to as a connection line). The data
separation block S60 calculates the slope of the connection line at
an intersection with the horizontal line of the threshold value
"B". The data separation block S60 determines whether or not the
calculated slope is steeper than a predetermined reference slope.
In the case where the calculated slope is steeper than the
predetermined reference slope, the data separation block S60 judges
that portions of the measurement data which indicate echo pulse
widths greater than the threshold value "B" are scatter-unrelated
signal components, and portions of the measurement data which
indicate echo pulse widths equal to or smaller than the threshold
value "B" are scatter-caused signal components. In the case where
the calculated slope is not steeper than the predetermined
reference slope, the data separation block S60 basically judges all
the measurement data to be scatter-caused signal components.
FIG. 13 shows the details of the data separation block S60. As
shown in FIG. 13, the data separation block S60 includes a step
S601 which follows the step S50 (see FIG. 6). Serial identification
numbers starting from "0" are assigned to segments respectively. A
variable "i" indicates the segment identification number. A segment
having an identification number "i" is also referred to as a
segment "i". The step S601 sets the segment identification number
"i" to "O". After the step S601, the program advances to a step
S603.
The step S603 determines whether a segment "i" is present or
absent. When the segment "i" is present, the program advances from
the step S603 to a step S604. On the other hand, when the segment
"i" is absent, the program advances from the step S603 to the step
S70 (see FIG. 6).
The step S604 determines whether or not the segment "i" satisfies
the following conditions B1 and B2.
B1 The transverse width W of the segment "i" is equal to or greater
than 2.5 m, and the segment "i" originates from echo beams in 15 or
more different angular directions.
B2 The beam order number corresponding to the left-hand edge of the
segment "i" is smaller than "10", or the beam order number
corresponding to the right-hand edge of the segment "i" is equal to
or greater than "95".
The above-mentioned conditions B1 mean that the segment "i" is
relatively great in transverse dimension. The above-mentioned
conditions B2 mean that a portion of the segment "i" is located at
a left-hand or right-hand edge portion of the detection area. The
left-hand edge potion corresponds to an angle of 1.5 degrees from
the left-hand edge of the detection area. The right-hand edge
potion corresponds to an angle of 1.5 degrees from the right-hand
edge of the detection area.
When the segment "i" satisfies the above-mentioned conditions B1
and B2, the program advances from the step S604 to a step S605.
Otherwise, the program jumps from the step S604 to a step S613.
The step S605 investigates the echo pulse widths represented by a
data portion corresponding to the range between the beam at the
left-hand edge of the segment "i" and the beam at the right-hand
edge of the segment "i", and searches the investigated echo pulse
widths for a peak one or a maximum one (see FIG. 14).
A step S607 subsequent to the step S605 sets the threshold value
"B" equal to the peak echo pulse width minus 64 nsec. A time
interval of 64 nsec corresponds to 10 LSB's since a 1 LSB is
equivalent to 6.4 nsec. The setting of the threshold value "B" is
based on the fact that echo pulse widths of scatter-unrelated
signal components are equal to or smaller than the peak echo pulse
width by less than about 64 nsec. The step S607 defines 83.2 nsec
(corresponding to 13 LSB's) as the lower limit of the threshold
value "B".
A step S609 following the step S607 forms the connection line by
connecting the graphic points (see FIGS. 12 and 14) which
correspond to the respective echo pulse widths. The step S609 forms
the horizontal line of the threshold value "B" (see FIGS. 12 and
14). The step S609 determines whether or not there are
intersections between the connection line and the horizontal line
of the threshold value "B" at two sides of the graphic point of the
peak echo pulse width. When there are intersections, the program
advances from the step S609 to a step S611. Otherwise, the program
advances from the step S609 to a step S615.
The step S611 processes the segment data corresponding to the
segment "i". Specifically, the step S611 discards portions of the
segment data which indicate echo pulse widths equal to or smaller
than the threshold value "B". On the other hand, the step S611
leaves portions of the segment data which indicate echo pulse
widths greater than the threshold value "B". FIG. 15 shows the case
where there are only two intersections QL and QR at the left-hand
and right-hand sides of the graphic point of the peak echo pulse
width respectively. In this case, the step S611 leaves portions of
the segment data which correspond to the range between the
intersections QL and QR. The step S611 discards other portions of
the segment data. Thus, the step S611 updates the segment data.
FIG. 16 shows the case where there are a plurality of intersections
at each of the left-hand and right-hand sides of the graphic point
of the peak echo pulse width. In this case, the leftmost one QLM is
selected from the intersections at the left-hand side of the
graphic point of the peak echo pulse width. Also, the rightmost one
QRM is selected from the intersections at the right-hand side of
the graphic point of the peak echo pulse width. The step S611
leaves portions of the segment data which correspond to the range
between the intersections QLM and QRM. The step S611 discards other
portions of the segment data. Thus, the step S611 updates the
segment data corresponding to the segment "i". After the step S611,
the program advances to the step S613.
The step S611 implements a discrimination between scatter-unrelated
signal components and scatter-caused signal components on the basis
of the previously-mentioned feature A1. The step S611 leaves the
scatter-unrelated signal components, and discards the
scatter-caused signal components.
The step S615 determines whether or not there is an intersection
between the connection line and the horizontal line of the
threshold value "B" at only one side of the graphic point of the
peak echo pulse width. When there is an intersection, the program
advances from the step S615 to a step S617. Otherwise, the program
advances from the step S615 to a step S621.
The step S617 calculates the slope of the connection line at the
intersection with the horizontal line of the threshold value "B".
The step S617 determines whether or not the calculated slope is
steeper than a predetermined reference slope. When the calculated
slope is steeper than the predetermined reference slope as shown in
FIG. 17, the program advances from the step S617 to the step S611.
In this case, the step S611 discards portions of the segment data
which indicate echo pulse widths equal to or smaller than the
threshold value "B", and leaves portions of the segment data which
indicate echo pulse widths greater than the threshold value "B".
Thus, the step S611 updates the segment data. On the other hand,
when the calculated slope is not steeper than the predetermined
reference slope as shown in FIGS. 18 and 19, the program advances
from the step S617 to a step S619.
The step S617 implements the slope calculation as follows. With
reference to FIG. 20, among all the graphic points of the echo
pulse widths, the step S617 selects three successive graphic points
at the left-hand side of the intersection and three successive
graphic points at the right-hand side of the intersection. The step
S617 may select only one or two successive graphic points at each
of the left-hand and right-hand sides of the intersection when a
complete set of three successive graphic points is unavailable. As
shown in FIG. 20, the step S617 calculates a straight line
approximate to the set of selected at most six graphic points
according to a least-squares method. The step S617 calculates the
slope of the straight line as an indication of the slope of the
connection line at the intersection.
The predetermined reference slope used by the step S617 corresponds
to 12.8 nsec per beam. The total number of the echo beams
corresponding to the selected graphic points is calculated by
referring to the beam order numbers. The difference between the
maximum and the minimum among the related echo pulse widths is
divided by the calculated total number of the echo beams. The
result of this division is a slope equal to a change in the echo
pulse width per beam.
When there are two or more intersections at only one side of the
graphic point of the peak echo pulse width, the step S617 selects
one from the intersections which is the farthest from the graphic
point of the peak echo pulse width. The step S617 implements the
previously-mentioned processing for only the selected
intersection.
The step S619 determines whether or not the beam order number
corresponding to the peak echo pulse width is in a predetermined
range representative of a portion of the detection area
sufficiently distant from its boundaries (edges). The lower limit
of the predetermined range is equal to a beam order number of "20".
The upper limit of the predetermined range is smaller than a beam
order number of "85". In other words, the predetermined range "PR"
is as "20.ltoreq.PR<85". When the beam order number
corresponding to the peak echo pulse width is in the predetermined
range, that is, when the graphic point of the peak echo pulse width
is sufficiently distant from the boundaries of the detection area,
the program advances from the S619 to the step S613. In this case,
all the segment data corresponding to the segment "i" remain as
they are. On the other hand, when the beam order number
corresponding to the peak echo pulse width is not in the
predetermined range, that is, when the graphic point of the peak
echo pulse width is near the boundaries of the detection area, the
program advances from the S619 to a step S625.
When it is difficult for the step S617 to calculate the slope of
the connection line at the intersection with the horizontal line of
the threshold value "B", the program advances from the step S619 to
the step S613 via the step S619. In this case, all the segment data
corresponding to the segment "i" remain as they are. It should be
noted that the step S617 can not calculate the slope when only one
graphic point is selectable.
In the case where only one side of the graphical point has an
intersection between the connection line and the horizontal line of
the threshold value "B", it is unclear which of a scatter-unrelated
signal portion and a scatter-caused signal portion the peak echo
pulse width corresponds to. To provide a discrimination between a
scatter-unrelated signal portion and a scatter-caused signal
portion, the slope of the connection line at the intersection with
the horizontal line of the threshold value "B" is calculated and
used. When the calculated slope is steeper than the predetermined
reference slope (see the step S617), it is determined that a
scatter-unrelated signal portion exists. On the other hand, when th
e calculated slope is not steeper than the predetermined reference
slope, it is determined that a scatter-caused signal portion
exists. A scatter-caused signal portion or portions are discarded
while a scatter-unrelated signal portion or portions are left.
The conditions that the calculated slope is not steeper than the
predetermined reference slope are also applied to the case where a
gentle variation in the echo intensity exists in a central portion
of the detection area. For example, when a preceding vehicle is
very close to the present vehicle and the detection area is fully
occupied by a reflector-free portion of the body of the preceding
vehicle, there is only a gentle variation in the echo
intensity.
In the case where the step S617 determines the calculated slope to
be not steeper than the predetermined reference slope and the step
S619 determines the graphic point of the peak echo pulse to be near
the boundaries of the detection area, the program advances to the
step S625. The step S625 deletes the segment data which corresponds
to the segment "i". After the step S625, the program advances to
the step S613.
Reflection of a scattered forward laser beam at an object outside
the detection area may cause the following wrong recognition. A
preceding vehicle on a lane adjacent to the lane along which the
present vehicle is traveling is erroneously recognized as a
preceding vehicle on the lane same as the present-vehicle's lane.
The combination of the steps S617 and S619 detects such conditions.
The step S625 deletes the segment data which corresponds to such
conditions. Accordingly, the above-indicated wrong recognition is
prevented.
The step S621 determines whether all the echo pulse widths are
smaller or greater than the threshold value "B". When all the echo
pulse widths are greater than the threshold value "B" as shown in
FIG. 21, the program jumps from the step S621 to the step S613. In
this case, all the segment data corresponding to the segment "i"
remain as they are. On the other hand, when all the echo pulse
widths are smaller than the threshold value "B" as shown in FIGS.
22 and 23, the program advances from the step S621 to a step
S623.
The step S623 is similar to the step S619. The step S623 determines
whether or not the beam order number corresponding to the peak echo
pulse width is in the predetermined range representative of the
portion of the detection area sufficiently distant from its
boundaries (edges). As previously mentioned, the lower limit of the
predetermined range is equal to a beam order number of "20". The
upper limit of the predetermined range is smaller than a beam order
number of "85". In other words, the predetermined range "PR" is as
"20.ltoreq.PR<85". When the beam order number corresponding to
the peak echo pulse width is in the predetermined range, that is,
when the graphic point of the peak echo pulse width is sufficiently
distant from the boundaries of the detection area, the program
advances from the S623 to the step S613. In this case, all the
segment data corresponding to the segment "i" remain as they are.
On the other hand, when the beam order number corresponding to the
peak echo pulse width is not in the predetermined range, that is,
when the graphic point of the peak echo pulse width is near the
boundaries of the detection area, the program advances from the
S619 to the step S625. In this case, the step S625 deletes the
segment data which corresponds to the segment "i". After the step
S625, the program advances to the step S613.
The combination of the steps S621, S623, and S625 prevent a wrong
recognition caused by reflection of a scattered forward laser beam
at an object outside the detection area.
The step S613 increments the segment identification number "i" by
"1". After the step S613, the program returns to the step S603.
Accordingly, signal processing about all the segments is
executed.
The laser radar sensor 5 corresponds to radar means. The object
recognition block 43 provided by the ECU 3 corresponds to
recognizing means. The steps and the block in FIG. 6 correspond to
the function of the recognizing means. The step S50 in FIG. 6
corresponds to the function of condition estimating means.
The vehicle control apparatus has advantages as mentioned below.
With respect to measurement data representing objects detected by
the laser radar sensor 5, it is possible to provide a suitable
discrimination between scatter-caused signal components and
scatter-unrelated signal components. Thus, it is possible to
prevent the accuracy of the object recognition from being decreased
by the difference between the actual shape of the cross section of
the forward laser beam and the theoretical shape thereof which is
used in the object recognition.
As shown in FIG. 6, the data separation block S60 is executed only
when the step S50 determines the windshield wiper switch 30 to be
in its on position. Therefore, an unnecessary anti-scattering
process can be prevented from being executed. In addition,
necessary signal portions for accurate object recognition can be
prevented from being deleted by the unnecessary anti-scattering
process.
The step S40 updates the threshold value "A" in response to the
size of a recognized object. The step S20 in FIG. 6 implements
deletion of components from the measurement data in response to the
updating-resultant threshold value "A". Therefore, the object
recognition can automatically follow actual conditions as mentioned
below. When the threshold value "A" is lower than the valley
between the second leftmost peak and the second rightmost peak as
shown in FIG. 10, the two preceding vehicles are recognized as a
single object having a transverse width greater than 2.6 m. As a
result, the threshold value "A" is periodically incremented on a
stepwise basis until the transverse width of a recognized object or
the transverse widths of recognized objects decrease below 2.6 m.
During this stage, when the threshold value "A" is greater than the
valley between the second leftmost peak and the second rightmost
peak, the two preceding vehicles are recognized as two separate
objects. When the threshold value "A" is increased to a suitable
value as shown in FIG. 11, the transverse widths of the two
recognized objects are smaller than 2.6 m. Provided that the data
separation block S60 is executed also, a vehicle having a width of
2 m can be recognized as an object having a width of 2 m. Even
during the stage until the step S40 controls the threshold value
"A" to a suitable value, an object width can be recognized and
detected by the data separation block S60.
Second Embodiment
A second embodiment of this invention is similar to the first
embodiment thereof except for design changes mentioned hereafter.
The second embodiment of this invention implements data separation
designed to compensate for the difference between the actual shape
of the cross section of a forward laser beam and the theoretical
shape thereof which is used in object recognition. Even in the
absence of scatter, superfluous light exits in a peripheral portion
of the forward laser beam. In the case of a millimeter wave beam, a
peripheral portion of the beam is relatively large. The wave
intensity of a peripheral portion of a beam is lower than that of
an inner portion of the beam. The data separation implemented by
the second embodiment of this invention is as follows. To provide a
discrimination between echo signal components related to a
peripheral portion of a beam and echo signal components related to
an inner portion of the beam, an echo signal is processed in
response to a reference intensity (a threshold intensity).
Specifically, echo signal components having intensities equal to or
higher than the reference intensity are selected and used as
effective signal components for object recognition. On the other
hand, echo signal components having intensities lower than the
reference intensity are discarded. For example, the reference
intensity is equal to a predetermined percentage of a peak
intensity (a maximum intensity). The above-mentioned data
separation is executed by a program block S150 indicated later.
FIG. 24 is a flowchart of a portion of a program for an ECU 3 (see
FIG. 1) which relates to object recognition in the second
embodiment of this invention. The program portion in FIG. 24 is
repetitively executed at a period corresponding to the period of
the scanning implemented by a laser radar sensor 5 (see FIG.
1).
With reference to FIG. 24, a first step S110 of the program portion
is similar to the step S10 in FIG. 6. A step S120 following the
step S110 is similar to the step S20 in FIG. 6. A step S130
subsequent to the step S120 is similar to the step S30 in FIG. 6. A
step S140 following the step S130 is similar to the step S40 in
FIG. 6.
After the step S140, the program directly advances to a data
separation block S150. The data separation block S150 corresponds
to the data separation block S60 in FIG. 6. The data separation
block S150 executes the previously-mentioned data separation in the
second embodiment of this invention. After the data separation
block S150, the program advances to a step S160. The step S160 is
similar to the step S70 in FIG. 6. After the step S160, the current
execution cycle of the program portion ends.
Third Embodiment
A third embodiment of this invention is similar to the first
embodiment thereof except that a sensor for detecting a raindrop
replaces the windshield wiper switch 30 (see FIG. 1). Generally,
the raindrop sensor is mounted on the body of a vehicle. In the
third embodiment of this invention, the step S50 (see FIG. 6)
determines whether the output signal of the raindrop sensor
indicates the presence or the absence of a raindrop. When the
output signal of the raindrop sensor indicates the presence of a
raindrop, the program advances from the step S50 to the data
separation block S60 (see FIG. 6). On the other hand, when the
output signal of the raindrop sensor indicates the absence of a
raindrop, the program jumps from the step S50 to the step S70 (see
FIG. 6).
* * * * *